My suggestion is keep the towed weight under the towing vehicle weight. Given the build of a Stagea I wouldn't want to tow too much with it.
That caravan pic from the UK is a joke, If a strong wind hit that van it'd pull the Stagea straight off the road.
I've seen a Stagea towing an R33. Got some wicked sway happening, dragged the arse of the Stagea all over the place.
That's just my opinion, but be sure to put some serious thought in to it. Because it'll be too late when it's all twisted